(a) Technical Field
The present disclosure relates to an apparatus and method for removing noise of an ultrasonic system to improve robustness against noise by removing external noise from a reception signal reflected from an object.
(b) Background Art
Generally, a reception ultrasonic signal reflected from an object has the same characteristics as a transmission ultrasonic signal. In other words, when reflected from an object, an ultrasonic signal does not undergo change in characteristics, such as frequency or waveform length, except for signal magnitude attenuation that corresponds to a medium. A system using an ultrasonic sensor, such as a Parking Assist System (PAS) or a Smart Parking Assist System (SPAS) calculates a distance from the medium using time of arrival of a transmission signal after reflection from the medium, and uses a Band Pass Filter (BPF) for removing external noise when the signal reflected from the medium is received.
Referring to FIG. 8, a conventional ultrasonic system includes an ultrasonic sensor 10 configured to sense a reception signal (e.g., received signal) reflected from a medium, a Band Pass Filter (BPF) 30 configured to remove external noise from the received signal, an amplitude modulator (AMP) 20 configured to modulate an amplitude of the received signal from which the external noise is removed, an edge detector 40 configured to remove a high-frequency component from an output value of the AMP 20, and a controller 50 configured to calculate a distance from the medium using a time difference between input time (e.g., reception time) of the received signal and output time (e.g., transmission time) of the transmitted signal. The conventional ultrasonic system detects an envelope of a received signal when a signal transmitted through an ultrasonic sensor is reflected from a reflector. When the detected envelope is greater than a predetermined value, an object is recognized and a corresponding alarm is generated or distance information is collected to perform a PAS or a SPAS function.
However, as shown in FIG. 9, when external noise greater than a predetermined value exists within a BPF frequency range, the conventional ultrasonic system recognizes that noise (that is, the external noise greater than the predetermined value which exists within the BPF frequency range) as a normal signal and generates an incorrect alarm. Accordingly, the conventional ultrasonic system performs signal transmission and reception twice to distinguish the external noise from the received signal. In other words, to determine whether the received signal reflected from an object once is a noise, signal transmission and reception are performed once more, to distinguish the external noise from the received signal. However, due to transmission and reception time of the ultrasonic signal and twice signal processing, a system delay occurs, causing potential performance degradation of the ultrasonic system. For example, when a vehicle using the ultrasonic system moves at a rapid speed, object recognition may be delayed due to system delay and thus correct information may not be provided to a driver.